Air suspension systems for vehicles have a plurality of air suspension bags supporting one or more vehicle axles in pairs on either side of each axle. In one well-known vehicle, the pairs of air springs are connected by a common large diameter air lines extending between correspondingly positioned air springs on adjacent axles. The common air lines are each connected by an air line to a height control valve directed to a respective side of a vehicle. The height control valve controls the air supply to the common air lines to adjust the inflation of the air springs to ensure that the vehicle is kept level as it is driven over variable road conditions. Unless defined otherwise, the term “height control valve” is used as equivalent to the term “leveling valve,” such that the terms “height control valve” and “leveling valve” may be used inter-changeably.
For example, when a vehicle negotiates a turn, the vehicle's center of gravity shifts along its width away from the turn. Due to the weight shift, the air springs on the side of the vehicle facing away from the turn start to contract, while the air springs on the side of the vehicle facing the turn start to extend. Consequently, the vehicle becomes unleveled from side-to-side. In response, one of the leveling valves on the lowered side of the vehicle supplies air to the contracted air springs, while the other leveling valve on the elevated side of the vehicle removes air from the extended air springs to keep the vehicle level. Through testing, it has now been found that leveling valves often overcompensate in responding to dynamic weight shifts of the vehicle, in which the air springs that were supplied air from the leveling valve tend to have a greater air pressure than the air springs that were purged by the leveling valve. As a result, a pressure difference persists between the two sides of the air suspensions system ever after the leveling valves attempt to level the vehicle. Even though a pressure differential remains between the air springs on opposite sides of the vehicle, the leveling valves return to a neutral mode (e.g., the rotary disk is set within a dead band range), in which there is a lack of pneumatic communication between the air springs on opposite sides of the vehicle. Due to this pressure differential between the air springs, the vehicle remains unlevel even after the leveling valves have adjusted the pressure of the air springs in response to the vehicle weight shift.
Other types of air suspension systems have replaced mechanical leveling valves with electronic-actuated valves to the control the height of the air bags. While some electronic-actuated valves have been designed to respond to vehicle weight shifts or vehicle rolling, electronic-actuated valves fail to account for pressure differentials between the air springs that persist after the heights of the air springs have been adjusted in response to vehicle weight shifts.
Accordingly, the present inventors have recognized that there is a need for an air management system that solves the problem of persistent pressure imbalance so that the vehicle may be restored to equilibrium air pressure, level and ride height.